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How to calculate distance in centimeters using IMDISTLINE?

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karishma
karishma on 4 Oct 2013
Commented: Image Analyst on 30 Jan 2021
i want to find out height of a sleeping infant. for that i want to find out the distance in cm. using 'imdistline' i'm getting the distance in pixels but how to convert that in cm?

Accepted Answer

Image Analyst
Image Analyst on 4 Oct 2013
Edited: Image Analyst on 4 Oct 2013
Put a ruler, a tape measure, a standard sheet of paper, or anything else of known length into the scene. Then snap a picture of it and use imdistline() to find the length in pixels. For example, let's say you laid down a sheet of A4 paper and measured it's distance as 2100 pixels. Knowing that it is 21 cm long, you get a spatial calibration factor of 21/2100, which you multiply your distances in pixels by to get the distance in cm. Multiply by that calibration factor squared to convert the area in pixels to the area in square centimeters.
calibrationFactor = 21/2100;
distanceInCm = distanceInPixels * calibrationFactor;
areaInSquareCm = areaInPixels * calibrationFactor ^ 2;
It's in the FAQ.
See my demo attached below for a really nice demo.
  3 Comments
Image Analyst
Image Analyst on 20 Nov 2014
Yes. You can do it. Just convert x in pixels to "real" x unit with its calibration factor. Then do the same for y with its calibration factor. Then use the Pythagorean theorem with the real x and real y.

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More Answers (2)

Roche de Guzman
Roche de Guzman on 30 Jan 2021
global h; h = imdistline; % activates the fx for drawing and measuring line
setLabelTextFormatter(h,'measure'); % message
addNewPositionCallback(h,@ShowDistance); % new position callback
%% Custom fx
function ShowDistance(pos)
global h xc yc; % sets line handles and x and y conversion factors to global
X = pos(:,1)*xc; Y = pos(:,2)*yc; % converts x and y positions from px to target unit
d = norm(diff([X Y])); % distance in target unit
setLabelTextFormatter(h,[num2str(d,'%.1f') ' target unit']); % updates measurement
end
  1 Comment
Image Analyst
Image Analyst on 30 Jan 2021
I like how you put in so many comments. I wish everyone would do that.

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Matt J
Matt J on 4 Oct 2013
Multiply by the length (in cm) of one pixel.
  9 Comments
leylin fatqiyah
leylin fatqiyah on 12 Feb 2015
this is my image https://www.mathworks.com/matlabcentral/answers/177673-how-to-measuring-curve-line-of-an-image
thank you

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